<?php
/**
 * CodeIgniter
 *
 * An open source application development framework for PHP
 *
 * This content is released under the MIT License (MIT)
 *
 * Copyright (c) 2014 - 2015, British Columbia Institute of Technology
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 *
 * @package    CodeIgniter
 * @author    EllisLab Dev Team
 * @copyright    Copyright (c) 2008 - 2014, EllisLab, Inc. (http://ellislab.com/)
 * @copyright    Copyright (c) 2014 - 2015, British Columbia Institute of Technology (http://bcit.ca/)
 * @license    http://opensource.org/licenses/MIT    MIT License
 * @link    http://codeigniter.com
 * @since    Version 1.0.0
 * @filesource
 */
defined('BASEPATH') OR exit('No direct script access allowed');

/**
 * CodeIgniter Encryption Class
 *
 * Provides two-way keyed encoding using Mcrypt
 *
 * @package        CodeIgniter
 * @subpackage    Libraries
 * @category    Libraries
 * @author        EllisLab Dev Team
 * @link        http://codeigniter.com/user_guide/libraries/encryption.html
 */
class CI_Encrypt {

    /**
     * Reference to the user's encryption key
     *
     * @var string
     */
    public $encryption_key        = '';

    /**
     * Type of hash operation
     *
     * @var string
     */
    protected $_hash_type        = 'sha1';

    /**
     * Flag for the existance of mcrypt
     *
     * @var bool
     */
    protected $_mcrypt_exists    = FALSE;

    /**
     * Current cipher to be used with mcrypt
     *
     * @var string
     */
    protected $_mcrypt_cipher;

    /**
     * Method for encrypting/decrypting data
     *
     * @var int
     */
    protected $_mcrypt_mode;

    /**
     * Initialize Encryption class
     *
     * @return    void
     */
    public function __construct()
    {
        if (($this->_mcrypt_exists = function_exists('mcrypt_encrypt')) === FALSE)
        {
            show_error('The Encrypt library requires the Mcrypt extension.');
        }

        log_message('info', 'Encrypt Class Initialized');
    }

    // --------------------------------------------------------------------

    /**
     * Fetch the encryption key
     *
     * Returns it as MD5 in order to have an exact-length 128 bit key.
     * Mcrypt is sensitive to keys that are not the correct length
     *
     * @param    string
     * @return    string
     */
    public function get_key($key = '')
    {
        if ($key === '')
        {
            if ($this->encryption_key !== '')
            {
                return $this->encryption_key;
            }

            $key = config_item('encryption_key');

            if ( ! strlen($key))
            {
                show_error('In order to use the encryption class requires that you set an encryption key in your config file.');
            }
        }

        return md5($key);
    }

    // --------------------------------------------------------------------

    /**
     * Set the encryption key
     *
     * @param    string
     * @return    CI_Encrypt
     */
    public function set_key($key = '')
    {
        $this->encryption_key = $key;
        return $this;
    }

    // --------------------------------------------------------------------

    /**
     * Encode
     *
     * Encodes the message string using bitwise XOR encoding.
     * The key is combined with a random hash, and then it
     * too gets converted using XOR. The whole thing is then run
     * through mcrypt using the randomized key. The end result
     * is a double-encrypted message string that is randomized
     * with each call to this function, even if the supplied
     * message and key are the same.
     *
     * @param    string    the string to encode
     * @param    string    the key
     * @return    string
     */
    public function encode($string, $key = '')
    {
        return base64_encode($this->mcrypt_encode($string, $this->get_key($key)));
    }

    // --------------------------------------------------------------------

    /**
     * Decode
     *
     * Reverses the above process
     *
     * @param    string
     * @param    string
     * @return    string
     */
    public function decode($string, $key = '')
    {
        if (preg_match('/[^a-zA-Z0-9\/\+=]/', $string) OR base64_encode(base64_decode($string)) !== $string)
        {
            return FALSE;
        }

        return $this->mcrypt_decode(base64_decode($string), $this->get_key($key));
    }

    // --------------------------------------------------------------------

    /**
     * Encode from Legacy
     *
     * Takes an encoded string from the original Encryption class algorithms and
     * returns a newly encoded string using the improved method added in 2.0.0
     * This allows for backwards compatibility and a method to transition to the
     * new encryption algorithms.
     *
     * For more details, see http://codeigniter.com/user_guide/installation/upgrade_200.html#encryption
     *
     * @param    string
     * @param    int        (mcrypt mode constant)
     * @param    string
     * @return    string
     */
    public function encode_from_legacy($string, $legacy_mode = MCRYPT_MODE_ECB, $key = '')
    {
        if (preg_match('/[^a-zA-Z0-9\/\+=]/', $string))
        {
            return FALSE;
        }

        // decode it first
        // set mode temporarily to what it was when string was encoded with the legacy
        // algorithm - typically MCRYPT_MODE_ECB
        $current_mode = $this->_get_mode();
        $this->set_mode($legacy_mode);

        $key = $this->get_key($key);
        $dec = base64_decode($string);
        if (($dec = $this->mcrypt_decode($dec, $key)) === FALSE)
        {
            $this->set_mode($current_mode);
            return FALSE;
        }

        $dec = $this->_xor_decode($dec, $key);

        // set the mcrypt mode back to what it should be, typically MCRYPT_MODE_CBC
        $this->set_mode($current_mode);

        // and re-encode
        return base64_encode($this->mcrypt_encode($dec, $key));
    }

    // --------------------------------------------------------------------

    /**
     * XOR Decode
     *
     * Takes an encoded string and key as input and generates the
     * plain-text original message
     *
     * @param    string
     * @param    string
     * @return    string
     */
    protected function _xor_decode($string, $key)
    {
        $string = $this->_xor_merge($string, $key);

        $dec = '';
        for ($i = 0, $l = strlen($string); $i < $l; $i++)
        {
            $dec .= ($string[$i++] ^ $string[$i]);
        }

        return $dec;
    }

    // --------------------------------------------------------------------

    /**
     * XOR key + string Combiner
     *
     * Takes a string and key as input and computes the difference using XOR
     *
     * @param    string
     * @param    string
     * @return    string
     */
    protected function _xor_merge($string, $key)
    {
        $hash = $this->hash($key);
        $str = '';
        for ($i = 0, $ls = strlen($string), $lh = strlen($hash); $i < $ls; $i++)
        {
            $str .= $string[$i] ^ $hash[($i % $lh)];
        }

        return $str;
    }

    // --------------------------------------------------------------------

    /**
     * Encrypt using Mcrypt
     *
     * @param    string
     * @param    string
     * @return    string
     */
    public function mcrypt_encode($data, $key)
    {
        $init_size = mcrypt_get_iv_size($this->_get_cipher(), $this->_get_mode());
        $init_vect = mcrypt_create_iv($init_size, MCRYPT_RAND);
        return $this->_add_cipher_noise($init_vect.mcrypt_encrypt($this->_get_cipher(), $key, $data, $this->_get_mode(), $init_vect), $key);
    }

    // --------------------------------------------------------------------

    /**
     * Decrypt using Mcrypt
     *
     * @param    string
     * @param    string
     * @return    string
     */
    public function mcrypt_decode($data, $key)
    {
        $data = $this->_remove_cipher_noise($data, $key);
        $init_size = mcrypt_get_iv_size($this->_get_cipher(), $this->_get_mode());

        if ($init_size > strlen($data))
        {
            return FALSE;
        }

        $init_vect = substr($data, 0, $init_size);
        $data = substr($data, $init_size);
        return rtrim(mcrypt_decrypt($this->_get_cipher(), $key, $data, $this->_get_mode(), $init_vect), "\0");
    }

    // --------------------------------------------------------------------

    /**
     * Adds permuted noise to the IV + encrypted data to protect
     * against Man-in-the-middle attacks on CBC mode ciphers
     * http://www.ciphersbyritter.com/GLOSSARY.HTM#IV
     *
     * @param    string
     * @param    string
     * @return    string
     */
    protected function _add_cipher_noise($data, $key)
    {
        $key = $this->hash($key);
        $str = '';

        for ($i = 0, $j = 0, $ld = strlen($data), $lk = strlen($key); $i < $ld; ++$i, ++$j)
        {
            if ($j >= $lk)
            {
                $j = 0;
            }

            $str .= chr((ord($data[$i]) + ord($key[$j])) % 256);
        }

        return $str;
    }

    // --------------------------------------------------------------------

    /**
     * Removes permuted noise from the IV + encrypted data, reversing
     * _add_cipher_noise()
     *
     * Function description
     *
     * @param    string    $data
     * @param    string    $key
     * @return    string
     */
    protected function _remove_cipher_noise($data, $key)
    {
        $key = $this->hash($key);
        $str = '';

        for ($i = 0, $j = 0, $ld = strlen($data), $lk = strlen($key); $i < $ld; ++$i, ++$j)
        {
            if ($j >= $lk)
            {
                $j = 0;
            }

            $temp = ord($data[$i]) - ord($key[$j]);

            if ($temp < 0)
            {
                $temp += 256;
            }

            $str .= chr($temp);
        }

        return $str;
    }

    // --------------------------------------------------------------------

    /**
     * Set the Mcrypt Cipher
     *
     * @param    int
     * @return    CI_Encrypt
     */
    public function set_cipher($cipher)
    {
        $this->_mcrypt_cipher = $cipher;
        return $this;
    }

    // --------------------------------------------------------------------

    /**
     * Set the Mcrypt Mode
     *
     * @param    int
     * @return    CI_Encrypt
     */
    public function set_mode($mode)
    {
        $this->_mcrypt_mode = $mode;
        return $this;
    }

    // --------------------------------------------------------------------

    /**
     * Get Mcrypt cipher Value
     *
     * @return    int
     */
    protected function _get_cipher()
    {
        if ($this->_mcrypt_cipher === NULL)
        {
            return $this->_mcrypt_cipher = MCRYPT_RIJNDAEL_256;
        }

        return $this->_mcrypt_cipher;
    }

    // --------------------------------------------------------------------

    /**
     * Get Mcrypt Mode Value
     *
     * @return    int
     */
    protected function _get_mode()
    {
        if ($this->_mcrypt_mode === NULL)
        {
            return $this->_mcrypt_mode = MCRYPT_MODE_CBC;
        }

        return $this->_mcrypt_mode;
    }

    // --------------------------------------------------------------------

    /**
     * Set the Hash type
     *
     * @param    string
     * @return    void
     */
    public function set_hash($type = 'sha1')
    {
        $this->_hash_type = in_array($type, hash_algos()) ? $type : 'sha1';
    }

    // --------------------------------------------------------------------

    /**
     * Hash encode a string
     *
     * @param    string
     * @return    string
     */
    public function hash($str)
    {
        return hash($this->_hash_type, $str);
    }

}
